1. Field of the Invention
The present invention generally relates to a Broadband Wireless Access (BWA) communication system, and in particular, to apparatus and method for adaptively applying a subchannel constitution scheme of a zone for relay service according to cell environmental variables in a multihop relay BWA communication system.
2. Description of the Related Art
One of the most important conditions of a 4th Generation (4G) communication system is a self-configurable wireless network configuration. The self-configurable wireless network refers to a wireless network which can provide mobile communication services by configuring the wireless network in an autonomous and distributive manner without control of a central system. Generally, in a 4G communication system, cells of a very small radius are installed to enable a high-speed communication and accommodate more traffic. In this case, it is anticipated that the centralized design of the 4G communication system is impossible. Accordingly, while being controlled and deployed in the distributive manner, the 4G communication system should be able to actively cope with environmental change such as joining of a new base station. To respond to this, a self-configurable wireless network is necessary in the 4G communication system.
In practice, to implement a self-configurable wireless network for the 4G communication system, a technique applied to an ad-hoc network needs to be adopted to the wireless access communication system. A representative case of this adoption is a multihop relay Broadband Wireless Access (BWA) communication system, where a multihop relay scheme of an ad-hoc network is applied to a BWA network including a stationary base station.
In a general BWA communication system, since communications between a fixed base station and a mobile station are executed through a direct link, a highly reliable wireless communication link can be easily established between the base station and the mobile station. However, since a position of the base station is fixed in a BWA communication system, wireless network configuration of the BWA communication system suffers low flexibility. As a result, it is hard for the BWA communication system to provide efficient communication services under radio conditions experiencing severe change of traffic distribution or other traffic conditions.
To overcome those shortcomings, BWA communication systems can utilize a relay service to deliver data in a multihop manner using neighbor mobile stations or relay stations. A multihop relay BWA communication system is able to reconfigure a network by promptly handling communication environmental changes and far more efficiently utilizing the entire wireless network. In addition, such a BWA communication system can provide a mobile station with a radio channel of better channel condition by installing a relay station between the base station and the mobile station and establishing a multihop relay path via the relay station. That is, the BWA communication system can provide a high speed data channel and extend a cell service coverage by providing services through the relay hop relay scheme via the relay station in a cell boundary region under poor channel conditions from the base station.
FIG. 1 shows conventional signal flows to provide service using a multihop relay scheme in a BWA communication system.
Mobile Stations (MSs) 140, 150, 160, and 170 in the multihop relay BWA communication system of FIG. 1 receive BWA services from Base Station (BS) 100 and Relay Stations (RSs) 110, 120, and 130.
The MSs 140 and 150 belonging to a service coverage 101 of the BS 100 communicate with the BS 100 using the direct MS link L1. The MS2 150, which resides in the cell boundary region of the BS 100 and suffers a poor channel status, receives a high data channel using a relay RS link L2 of the RS2 130.
The MSs 160 and 170 out of a service coverage 101 of the BS 100 communicate with the BS 100 using a relay RS link L3 of the RS1 110. In other words, the BS 100 can extend its service coverage using the RS1 110 by providing a communication link to the MSs 160 and 170 outside the service coverage. The MS4 170, which lies in the cell boundary region of the service coverage of the RS1 110 and suffers a poor channel status, can increase transmission capacity using the relay RS link L4 of the RS2 120.
As described above, a BWA communication system can achieve a cell coverage extension and a capacity increase by providing a control channel and a high data channel to MSs in a cell boundary region and a shadow area under poor channel conditions by use of a multihop relay scheme via a RS.
Recently, in BWA communication systems, research on Orthogonal Frequency Division Multiple Access (OFDMA) schemes are progressing. When a BWA communication system adopts an OFDMA scheme, by dividing an entire frequency band into a plurality of orthogonal subcarriers, a variety of subchannels can be constituted according to a subcarrier allocation scheme. For example, Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard defines subchannel allocation schemes of Partial Usage Sub-Channel (PUSC), Full Usage Sub-Channel (FUSC), Optional FUSC (OFUSC), Adaptive Modulation and Coding (AMC) subchannel, Tile Usage Sub-Channel 1 (TUSC1), and TUSC2.
Hence, a BS using a OFDMA scheme can communicate using a subchannel constitution scheme suitable for cell environmental variables, such as channel condition, interference, mobility, etc.
FIG. 2 shows a conventional frame constructed using a plurality of subchannel constitution schemes in an IEEE 802.16 system. The IEEE 802.16 system of FIG. 2 adopts an OFDMA scheme.
The frame of FIG. 2 is divided to a DownLink (DL) subframe 200 and an UpLink (UL) subframe 201.
The DL subframe 200 places preamble and common control information at fixed positions (mandatory slots) of the front end. The common control information uses a fixed subchannel constitution scheme. For instance, an IEEE 802.16 system may fix the common control information in a PUSC zone.
The common control information includes a Frame Control Header (FCH). The FCH is information for decoding the control information (=DL map) relating to the DL subframe 200 in the common control information.
A receiver, which receives the DL subframe 200 from a transmitter, can decode the control information relating to the DL subframe 200 only by decoding the FCH.
Next, by checking the control information, the receiver can acquire subchannel constitution scheme information with respect to a plurality of zones of each subframe (DL/UL subframes). The receiver can acquire the subchannel constitution scheme information of each zone from an IE (Information Element) {e.g., STC_DL_Zone-_IE( ), UL_Zone_IE( ) or AAS_DL/UL_ZoneIE( )} containing zone information of the control information.
In FIG. 2, the zone drawn with a solid line uses a fixed slot using a fixed subchannel constitution scheme, and a burst zone drawn with a dotted line can change its size and subchannel constitution scheme according to the cell environment.
To support a multihop relay service in a BWA communication system, the BS needs to communicate with not only the MS but also the RS. Accordingly, the BS communicates with the MS and the RS using a frame structure as shown in FIG. 3.
FIG. 3 shows a conventional frame structure of a multihop relay BWA communication system.
In the frame of FIG. 3, DL subframe 300 and UL subframe 310 includes direct link areas 301 and 311 for communications between a BS and an MS, and indirect link areas 303 and 313 for communications between the BS and an RS.
The BS provides a sync channel, a control channel, and a traffic channel to MS connected in the direct link using the direct link area 301 of the DL subframe 300. The BS provides a sync channel, a control channel, and a traffic channel to the RS using the indirect link area 303 of the DL subframe 300. The sizes of the direct link area 301 and the indirect link area 303 may be fixed or adaptively adjusted according to the cell environment.
When a BWA communication system performs communication using the frame of FIG. 3, the RS, like the MS, communicates with the BS using the direct link area 301 at the initial access. Next, the RS is assigned a start symbol position of BS-RS link using the indirect link area 303 to provide the relay service. In doing so, the RS can decode signals transmitted at a start symbol position of the indirect link area 303 by decoding the FCH of the indirect link area 303. The RS needs to acquire the subchannel constitution scheme of the zone including the FCH to decode the FCH. However, if the sizes of the direct link area 301 and the indirect link area 303 are adaptively adjusted according to the cell environment, the RS cannot acquire the subchannel constitution scheme information of the start zone of the indirect link area 303.
As discussed above, a BWA communication system is capable of adaptively adjust sizes of a first area for a direct link and a second area for an indirect link according to a cell environment. In this case, a subchannel constitution scheme including a start point of a second area can be changed as well. Therefore, a need exists for a method enabling an RS to detect a subchannel constitution scheme of a start position of a second area in a BWA communication system.